CCI DRAG®

DA-90DSV Attemperator

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2 DA-90DSV Attemperator application discussion

n Minimizes Leakage

n Handles High Thermal Stresses

n Enhanced Controllability

n Prevents Cavitation Damage

n Meets Common Face-to-Face Dimensions

n Low Maintenance Costs

n Less Erosion Damage

n High Plant Efficiency

Figure 1: Typical HRSG schematic

With each new operating season, the limits of interstage attemperators in

Heat Recovery Steam Generators (HRSGs) are being tested. As plants search

for the most economical operation, be it cycling daily or operating at reduced

loads for extended hours, reliability and operability of the superheat (SH)

and reheat (RH) interstage attemperators consistently come into question.

Whether it is a constantly leaking attemperator that must be repaired or

replaced every outage, or a more catastrophic failure like a boiler tube leak

or a ruptured steam line, the headaches and frustrations associated with

interstage attemperation are becoming all too familiar to plant managers,

operators, and maintenance personnel.

Flash Vessel

Spraywater

DA-90 DSV SH-InterstageAttemperator

Economizer

Reheater

Reheater

Superheater

Superheater

Steam Generator

Boiler

DA-90DSV RH-InterstageAttemperator

Spraywater

IP/LP Turbine

HP Turbine

HRSG

From HPTurbine Exhaust

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SH1 outlet SH2 inlet Final steam Spraywater flow

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SH1 outlet SH2 inlet Final steam Spraywater flow

Figure 2: Illustrations of damage due to thermal cycling, often caused by poor attemperator performance.

Symptoms of Faulty Attemperators

Some of the first signs of trouble start with uncontrolled spraywater flow and

leakage. Scheduled inspections often reveal:

nDamaged spray nozzles.

nCracked attemperator housings.

nDamaged seals.

nCracked steam pipes and boiler tubes.

nCracked/broken thermal liners.

The root cause of most interstage attemperator problems can be traced to four

main system/installation parameters:

nHigh pressure drop through the spraywater control portion of the attemperator.

nHigh thermal stresses caused by large temperature differences between the steam and the cooling water.

nPoor atomization of the cooling water leading to large amounts of unevaporated water in the steam line.

nPoor installation with short distances to downstream elbows, temperature sensors, or HRSG reentry points.

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SH1 outlet SH2 inlet Final steam Spraywater flow

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3DRAG® DA-90DSV Attemperator

Faulty Attemperator Design

Many of the common interstage attemperator systems overlook several or

all of the root causes of failure listed on the previous page. Such designs

will lead to problems in your plant, it’s only a matter of time! Consider

the following:

Single Stage Pressure Drop – Problem

When using fixed speed pumps, the pressure drop in some interstage

attemperator spraywater systems can reach levels greater than 2000 psi

(133 bar). This high pressure drop will severely damage and prematurely

wear a single stage control element causing wire draw, leakage, and

cavitation damage (See Figure 3). The key to eliminating this root cause

of failure is to incorporate multiple stages of pressure drop in a control

valve trim. CCI’s DRAG® Velocity Control Trim can easily package up to

20 stages of pressure drop in attemperator systems to handle the large

pressure drop of the spraywater system.

Valve Trim in the Steam Flow – Problem

As allowable operating temperatures increase, interstage attemperators

can see steam to spraywater temperature differences near 700 F (390 C).

This high temperature difference in conventional attemperator designs

will lead to high thermal stresses. An attemperator design, such as the

one shown in Figure 4, that locates tight clearance control elements (i.e.

valve trim) in an environment that sees these drastic temperature swings

will fail. Common failures such as cracked attemperator bodies, cracked

attemperator welds, cracked attemperator nozzles, stuck or seized plug

and stem elements, and even packing leaks can all be attributed to a

design that neglects to account for the high temperature difference in this

application. To avoid these problems, location is the key. Tight clearance

valve trim components should be moved out of the steam pipe and away

from the hot steam temperatures.

Pressure Boundary and Tack Welds – Problem

Due to the nature of the application and the operation of today’s HRSGs,

interstage attemperators will always be exposed to thermal cycling. Welds,

and the heat affected zones around them, are vulnerable to cracking when

put through thermal cycles while also being exposed to high pressure

loads and bending stresses. A properly designed interstage attemperator

eliminates all welds by using a one-piece Chrome Moly forging, thus

removing the risk of cracking in the attemperator body.

Problems Solution

High pressure drop in a single stage Use multiple stages of pressure drop in a DRAG® Velocity Control Trim

Expose attemperator to high thermal stresses by locating trim components in the hot steam pipe

Move the valve trim to a safer environment outside of the steam pipe and away from harsh thermal stresses

Use pressure boundary and tack welds Eliminate all welds by using a one-piece Chrome Moly forging

Figure 3: Cavitation damage on plug.

Figure 4: Section view of a conventional attemperator design.

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4 DRAG® DA-90DSV Attemperator features

Benefits DRAG®

DA-90DSV Competition

n Provides the Valve Doctor Solution. CCI works with plant operators to improve plant performance, reliability and output.

n Prevents Cavitation Damage. CCI works in accordance with ISA guidelines to ensure cavitation is avoided.

n Eliminates Erosion Damage. By controlling fluid velocities, erosion is eliminated.

n Thermal Stress Analysis. CCI accounts for all thermal stresses in the attemperator design.

n Stops Costly Maintenance Cycles. CCI valves are designed

and sized to provide longer intervals between maintenance and allows easy access to all components.

n Eliminate Thermal Damage to the Trim. Control element is outside of hot steam flow.

n Proven Desuperheating Experience.

Benefits DRAG®

DA-90DSV Competition

Multi-stage DRAG® Disk Stack Technologies

Limits fluid velocities, controls vibration and erosion. Multiple Cv trims throughout disk stack allows characterized design for

optimum control throughout operating conditions.

Stem Packing

Graphite packing is standard for high temperature service.

Water Inlet

Customer Connections

Class V Shut-off

A metal seat is standard, with

a 500 PLI (9 kg/mm) loading force

to achieve tight shut-off.

Disk Stack Labyrinth

Grooves

This section of the disk stack

has no flow passages; in

their place labyrinth

grooves break up clearance

flow, preventing seat ring damage.

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5Use check list to evaluate the benefits of CCI’s DRAG® DA-90DSV Attemperator

Spray Nozzle

The variable orifice spray nozzle used in the DA-90DSV provides excellent primary atomization and high rangeability. The design is proven through decades of installation in high temperature steam applications. Multiple nozzle designs (as pictured) are available for high capacity installations.

n Thermal Stress Analysis. CCI accounts for all thermal stresses in the attemperator design.

n Stops Costly Maintenance Cycles. CCI valves are designed

and sized to provide longer intervals between maintenance and allows easy access to all components.

n Eliminate Thermal Damage to the Trim. Control element is outside of hot steam flow.

n Proven Desuperheating Experience.

Benefits DRAG®

DA-90DSV Competition

No Trim in Steam Flow

Many probe designs place valve trims in the steam flow, exposing them to high steam temperatures

and very large thermal stresses. The DA-90DSV moves all tight

clearance trim components out of the steam flow and out of the

harmful thermal environment.

Tapered Profile

The attemperator is designed with a tapered profile to minimize any

vibrations caused by harmonic frequencies associated with

vortex shedding. This becomes especially important as pipe sizes

increase and the length of the attemperator increases.

Forged Design

A fully forged one-piece Chrome Moly design eliminates the need

for welding, and eliminates the risk of welds failing due to the

high thermal cycling and stress of the surrounding environment.

Stem Packing

Graphite packing is standard for high temperature service.

Water Inlet

Customer Connections

LowFlow

HighFlow

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6 DA-90DSV Attemperator Solutions

Figure 6: Characterized Equal Percentage DRAG® disk stack trim.

Eliminate Cavitation with DRAG®

DRAG® trim forces the fluid to travel through a torturous path of turns

(Figure 5). Each turn causes a pressure loss in the fluid, and the pressure

gradually reduces as the fluid flows through the multiple turns. This series

of multiple pressure drops controls the fluid velocity and allows the pressure

to reduce without falling below the vapor pressure, thus avoiding cavitation

and the destruction to the valve and trim that can come with it. The DRAG®

multistage pressure drop trim provides a clear benefit in terms of performance

and maintenance costs when cavitation is a concern.

Accurate Control and Reliable Operation at all Flow Conditions with the CCI DRAG® Disk Stack

DRAG® disk stacks can be customized to provide the required Cv throughout

the valve stroke. This is accomplished by configuring disks with various

numbers of turns within the stack (Figure 6). Thus, the DRAG® control valve

disk stack can be designed for many different flow characteristics, i.e. linear,

equal percentage, or modified equal percentage (Figure 6). The disks at the

bottom of the disk stack, close to the valve seat, are equipped with a higher

number of pressure letdown stages (up to 20 stages or more) to provide

critical protection of the seating surfaces on the plug and seat ring. As the

valve strokes open, fewer pressure letdown stages are used for more capacity

as the process requires, providing good control over the entire range of flow

conditions. Independent and isolated flow paths are used to eliminate short

circuits between flow paths and provide the best result in pressure letdown.

Reliable Long Term Shutoff

The DRAG® control valve uses a hard seat material and a very high seat loading

to provide reliable and repeatable long term shutoff in very high pressure

differential applications. The actuator is sized to provide a minimum seating

load of 500 lb/in (9 kg/mm) of seat ring circumference, as recommended by

ISA guidelines. The DRAG® velocity control trim design, combined with the

high seating force for shut-off, protects the seating surfaces from cutting and

pitting due to erosion or wire draw.

Benefits of DRAG® Velocity Control Trim

n Prevents Cavitation Damage

n Improves Plant Performance

n Eliminates Erosion Damage

n Lowers Operating Costs

n Reduces Maintenance Costs

n Reduces System Complexity

n Avoids Plant Shutdowns

n Provides Accurate Temperature Control

% Flow100

908070605040302010

00 10 20 30 40 50 60 70 80 90 100

% Stroke

Modified Linear

Linear

Modified Equal %

Figure 5: Each turn in the DRAG® trim is a single stage of pressure drop, eliminating potentially harmful kinetic energy.

Multiple Inlet Flow Channels

Pressure Equalizing Ring (PER) Grooves

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6” (153mm) MIN C

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STEAM CONNECTION

WATER INLET

HEIGHT

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Technical Specifications

No Name Material

1 Body ASME-SA217-WC9/C12A

2 Bonnet ASME-SA182-F22/F91

3 Spindle INCONEL 718

4 Guide Bushing 300 SS

5 Gaskets Graphite/300 SS

6 Seat 300 SS

7 Disk Stack INCONEL 718

8 Packing, Stem Graphite

9 Packing, Spacer Carbon

10 Yoke Carbon Steel

11 Nozzle Housing ASME-SA182-F22/F91

12 Spray Nozzle ANSI 616

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ØD MIN BORE

Trim SizeWater Flange

Steam Flange

ANSI A B CDia. D(4) Height (2) Weight

3/8”, 5/8”, 1” (10, 15, 25)

1.5” RF (40)

3.0” RF (80)

600-15009.0” (229)

6.0” (152)

19.7” (500)

2.9” (73.7)

34” (865)

~300 lbs (140 kg)

25009.5” (241)

7.0” (178)

1.5” (40)

2.5” RF (65)

4.0” RF (100)

600-250012.25” (311.2)

12.25” (276.4)

3.81” (96.8)

51” (1295)

~500 lbs (230 kg)

Nom. Pipe Dia.Length

(see note 3 & 6)

10-14”(250-350) 14.12”(358.6)

16-20”(400-500) 17.75”(450.8)>20” (>500) 21.25” (539.8)

Notes:1. Contact factory for other sizes2. Given is maximum; add 15” (380 mm) for manual override3. Customer flange height will vary to center nozzle(s) in steam pipe4. Customer supplied flanged connection5. Numbers in brackets give dimensions in millimeters6. Custom probe lengths available for retrofit projects

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Contact us at: info@ccivalve.com

For sales and service locations worldwide, visit us online at: www.ccivalve.com

Throughout the world, customers rely on CCI companies to solve their severe service control valve problems. CCI has provided custom solutions for these and other industry applications for more than 80 years.

DRAG is a registered trademark of CCI.©2007 CCI 880 11/07 5K